What compression?
Turbo Mini Forums

hi guys i am new to the forum, and i have aquestion i don't know if anyone can help me?
i decided the other day to purchase myself a supercharger kit for my Mpi mini, i have been having a little trouble with the gearbox so i have got to take the engine out to see wats going on it there. Seen as the engine is out i decided that i want to get the proper set up to get the most out of the charger, i'm wandering what pistons i should get, because i know you need to lower the compression to handle the boost?
Also would the compression ratio be affected if i add the 15% smaller pulley on the supercharger?
Thanks

the best thing to do first is do a search on compression or pistons c/r :)

1293 Turbo mini

Hi,
Worms, can of, open...
You need to know how much boost you're going to run.
You need to know what the change in pulley is going to do to the charger output.
Intercooler?
That's just the tip of the iceberg....
Cheers,
Gavin :)

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ah i see is there anyway of finding out what PSI a bini supercharger puts out?

Edited by Paul S on 6th Jan, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

When i was browsing around the internet i found some information on the eaton supercharger, i not sure how acurate it is but it said that with the standard bini pulley on it it puts out 11.6 Psi and with the 15% smaller pulley it would be 14.5Psi, does this sound right because i put it into the calculator and it was stating about 154 BHP with the smaller pulley

M45's don't like high boosts, but maybe you'd get away with it a tad running suck through, might improve the efficiency of the blower. However, the map doesn't look good for a dP of 12psi when you run it dry. I'm wondering if you could add a bit of ethanol and use the dHv of that to take up a bit of the heat.

I would say that from my buggerings about, a longer cam and more revs is a better way to skin the cat, along with less boost. Otherwise you are starting to get in the sap territory.

What pulley are you using on the bottom? (Zetec?)

Bugger off, I'm getting there.

i was just using the standard one, lol as you can tell i am a little new to this subject

Have a look at doing what you're doing but using an avonbar Ph2 cam. It's like a 276 for SC engines. You need the extra exhaust lift/duration in my opinion to run the inlet closure a tiny bit more early, which allows you to get more power. It's been a while since I thought about blower theory a lot but having a high trapping efficiency relies on having a relatively early inlet valve close and enough time to clear everything else. In my opinion, I think the A Series is under exhausted and in order to maximise the engine (with a blower) you have to get everything out as quickly and as totally as possible, whilst minimising overlap yet giving everything a chance to "gasp" properly.

I'm sure there are people on here who would be ready to disagree, but if you want to pass more gas, using conventional cams, you start to get too much inlet duration at the sacrifice of overlap with insufficient exhaust duration/lift with longer cams. This isn't so bad with Kent Cams as they often have longer exhausts, but Piper 270's and 286's are symmetrical, which in my terms means that they have too much inlet and not enough exhaust.

My blower is sat in the garage and my mini is now without engine in the shed. Says a lot about my approach! Too much talk and not enough action. Too many other things to do.

I can't remember what the MPi cam is, but In know that the SPi cam is a very good one for a blower. You would need to run slightly bigger inlet valves to get the best out of it with high boosts, moderate port sizes to give you an average gas speed but the all important exhaust "flow" is great. It's not one I would go for out of the box, unless I had a 37mm inlet race head which was over-skimmed and then I'd use a decompression plate, which I am a huge fan of, for several reasons. :)

Bugger off, I'm getting there.

Still a little confused, what piston do you turbo guys use under what boost?

How long is a piece of string?

Ranges from standard turbo pistons and 4psi right the way through to 18cc forged pistons and 25+psi.

Depends entirely on budget in all honesty.

is there anyway to calculate what pistons for which boost pressure? for example i posted earlier i read that the bini blower with the 15% reduction would put out about 14.5 Psi so which pistons would i use for this?

There is a graph that was posted which showed the relationship between fuel octain rating, boost pressure and compression. Try searching for "compression ratio" "CR" etc and you will find it. It's a rough guide and dosen't take into acount charge temps etc.

I am planning on running 15 psi (with a turbo) and with a decent intercooler and compression in the low 8's. Apporximately 11-14cc piston dish and a 27cc head gives this (cast omega pistons are 11cc). BUT your talking supercharger here and you haven't said if it's suck through or blow through. Suck through is a different kettle of fish as you can't intercool the intake charge.

this thread is usefull for the compression ratio as there is a handy table to help.

What is the engine to be used for? daily hack or balls to the wall max revs track abuse.

Edit: Bugger I forgot to paste the link in. Paul has pasted it in his response below anyway:$

Edited by minimole23 on 15th Jan, 2008.

Try this:



I would suggest lowering the compression ratio another 1.0 if you do not plan to use an intercooler.

Then use this:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ok guys i have been looking at all of the infor you have been giving me, and using the blower calculator, if i was to use the JE 18cc pistons, with a drive ratio of 2.18 according to the calculator this would be about 20Psi of boost giving around 180hp is this a unreasonable power out put, is my head in the clouds a little bit?

If you're planning on running 20psi you'll need to uprate more than your pistons, something like 10psi would be a lot more sensible. At that kind of boost a decent set of cast pistons will do the job just fine.
Also what supercharger are you going to use ? I know most of the commonly used ones will not be efficient running at that kind of boost {20psi}. :)

Edited by Turbo Phil on 17th Jan, 2008.

WWW.TURBO-MINI.COM

I'm with phill on this. Assuming you are planning on using an Eaton M45 (MINI) then at 10 psi you are looking at a minimum temp increase (from ambient) of 65 degrees. There is no info for pressures above 10psi, but it's only going to get a shit load worse.

Assuming no intercooler, you won't make it to the end of your drive before det melts the pistons!

You need a turbo for 180 bananas

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

i see well i have just plumed 16Psi into the calcutor and is gives figures of about 170 so that sound pretty good to me. In terms of upgrading the internals what do i need to look at? i think i am going to use the JE 18cc pistons but what else do i need to consider?
Thanks for your help guys if i had just gone with what i know it could have been a big old melted mess!

You can put 16psi into any calculator and have it tell you what you want, but an eaton M45 blowing 16psi will not make that power, no matter what intercooler you use. as stated, they ain't suitable for high boost. I also don't like the idea of running fuel through them as this will ultimately lift the coating off the rotors.

The JE pistons sit a long way down the bores as well - so you need a heavy block skim, or your CR will be around 1.5 less than you think!

Edited by turbodave16v on 17th Jan, 2008.

i see well i have just plumed 16Psi into the calcutor and is gives figures of about 170 so that sound pretty good to me. In terms of upgrading the internals what do i need to look at? i think i am going to use the JE 18cc pistons but what else do i need to consider?
Thanks for your help guys if i had just gone with what i know it could have been a big old melted mess!

http://theoldone.com/articles/damaged%2Dblower/

read and rethink..

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Ok guys can someone surggest the setup i should run for good horsepower output, ie pistons and what psi i should put out of the charger?

Ok guys can someone surggest the setup i should run for good horsepower output, ie pistons and what psi i should put out of the charger?

Ok guys can someone surggest the setup i should run for good horsepower output, ie pistons and what psi i should put out of the charger?